1. Field of the Invention
The present invention relates to illumination apparatuses as well as cameras equipped with an illumination apparatus, and in particular to illumination apparatuses, in which the length, in vertical direction of the apparatus, of the outgoing aperture portion through which light is emitted from the illumination apparatus is shortened without making the overall shape of the apparatus larger.
2. Description of Related Art
Illumination apparatuses used for cameras and the like are conventionally configured with a light source and an optical component such as a reflective mirror or Fresnel lens that guides the light rays emitted from the light source to the front of the apparatus (i.e. toward the object).
Regarding such illumination apparatuses, there have been various proposals for condensing the light rays that are emitted from the light source into various directions with high efficiency to the necessary illumination range. In particular in recent years, apparatuses have been proposed with which an improvement of the condensing efficiency as well as a miniaturization of the apparatus can be attained by placing an optical member utilizing total reflection, such as a prism light guide, instead of a Fresnel lens that is placed at the front of the apparatus with respect to the light source.
As one such apparatus, Japanese Patent Application Laid-Open No. H4 (1992)-138438 (referred to as “Document 1” in the following) discloses an illumination optical system that condenses light rays emitted from a light source to the front of the apparatus with a lens having positive refractive power, while directing the light rays that have been emitted from the light source toward the side of the apparatus to the front of the apparatus and condensing them by a total-reflection surface at which they are reflected, thereby irradiating illumination light from the same outgoing surface. That is to say, there are illumination optical systems using a prism making it possible to achieve miniaturization and increase the condensing efficiency, in which those of the light rays that are emitted from the light source whose optical path has been divided at an ingoing surface position of an optical member are emitted from the same outgoing surface,
As an improvement of this illumination optical system, Japanese Patent Application Laid-Open No. H8 (1996)-262537 (referred to as “Document 2” in the following) proposes an apparatus in which miniaturization of the entire illumination optical system is achieved by placing the prism in front of the light source in the apparatus, and in which the surface of the prism that emits the totally reflected light is tilted with respect to the optical axis.
On the other hand, in illumination apparatuses of the type in which the irradiation angle range of the illumination light is fixed, in the tele state in which the necessary irradiation angle range is narrow as the image-taking optical system has been zoomed to a high zoom ratio, illumination light is irradiated onto an unnecessary range, which leads to a large energy loss. In order to address this problem and to eradicate the energy loss, several illumination apparatuses with variable irradiation angle have been proposed, with which the irradiation angle range of the illumination light can be changed in accordance with a change of the image-taking range (zooming of the image-taking optical system).
In one such illumination apparatus, the irradiation angle range of the illumination light is changed by moving a first optical member and a second optical member to change the spacing between them. More specifically, as disclosed in Japanese Patent Application Laid-Open No. 2000-298244 (referred to as “Document 3” in the following), the first optical member converts light rays emitted from the light source to the front of the apparatus into light rays of an optical axis direction, and includes a convex lens serving as a portion of the ingoing surface, a total reflection surface that converts light rays emitted from the light source to the side of the apparatus by total reflection into light rays of the optical axis direction, and an outgoing surface made of a plurality of small lenses.
The second optical member includes, on an ingoing surface onto which the light emitted from the first optical member is incident, a plurality of lenses that cancel the refractive power of the small lenses of the first optical member. Moreover, the irradiation angle range of the illumination light can be changed by moving the above-described first optical member and the second optical member relative to one another.
In recent years, as camera bodies become smaller, there is a need for making illumination optical systems that are mounted on the camera body and serves as an auxiliary light source even smaller. To address this, Documents 1 and 2 etc. propose illumination optical systems that strive for miniaturization and higher performance by using prisms of the above-described types.
On the other hand, in order to adapt to new camera designs, there is a strong demand for further improvements of these illumination optical systems, and in particular for a smaller aperture portion (in the vertical direction of the camera) serving as the light emission region that is apparent from the outside of the product (camera). That is to say, there is a demand for making only the aperture portion of the illumination apparatus smaller, while making the illumination apparatus smaller by using prisms as in the conventional technology, which is a very difficult demand that could not be realized with the prior art.
In the illumination optical systems of both Document 1 and Document 2, the portion where the total reflection surface is broadest serves as the opening (aperture) of the illumination optical system, and making the aperture portion smaller was not possible by a mere extension of the conventional approach without severely lowering the optical characteristics (light distribution characteristics).
Moreover, the demand to make the aperture portion of the illumination apparatus smaller is not restricted to the above-described illumination apparatuses in which the irradiation angle range of the illumination light is fixed, and the same demand is also strong for illumination apparatuses in which the irradiation angle range can be changed.
However, as can be understood from the illumination apparatus of the light-guide type disclosed in Document 3, the size of the aperture portion in conventional illumination apparatuses of the type with variable irradiation angle needs to be approximately the same size as the aperture portion (outgoing surface of the first optical member) that is formed by the portion where the total reflection surface is broadest, and the aperture portion of the illumination apparatus cannot be said to be sufficiently small. Also most of the other illumination apparatuses of the type with variable irradiation angle, the aperture portion of the illumination apparatus (optical member) needs to be much broader than the reflection screen for condensing, and by a mere extension of the conventional approach, a further miniaturization of the aperture portion is not possible without considerably lowering the optical characteristics.